Solvent deasphalting process

ABSTRACT

AN ASPHALTENE-CONTAINING CHARGE STOCK IS SUBJECTED TO SOLVENT DEASPHALTING TO PROVIDE A RESIN- AND ASPHALTENECONTAINING, SOLVENT-LEAN HYDROCARBON PHASE. THIS SOLVENTLEAN PHASE IS SUBJECT TO A SECOND SOLVENT DEAPHALTING TECHNIQUE IN ORDER TO COVER A RESIN CONCENTRATE AND TO REJECT AN ASPHALTIC PITCH.

Aug. 20, 1974 J. G. GA'rsls SOLVENT DEASPHALTING PROCESS Filed Sept. 18. 1972 IIAV kuub@ k mum Emi Em @En QQ United States Patent O 3,830,732 `SOLVENT DEASPHALTING PROCESS John G. Gatss, Des Plaines, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill. Filed Sept. 18, 1972, Ser. No. 289,925 Int. Cl. Cg 31 14 U.S. Cl. 208--309 6 Claims ABSTRACT OF THE DISCLOSURE APPLICABILITY OF INVENTION The invention herein described is intended to be utilized for the removal Iof hydrocarbon-insoluble asphaltenic material from petroleum charge stocks containing the same. More specifically, my invention is directed toward a process for deasphalting atmospheric tower bottoms, vacuum tower bottoms (vacuum residuum), crude oil residuum, topped crude oils, coal oil extract, oils recovered from tar sands, etc., all of which have come to be referred to in the art as black oils and which contain varying quantities of asphaltic material.

Hydrocarbonaceous crude oils, and particularly the heavier oils extracted from tar sands, reduced crudes and vacuum residumm, contain high molecular Weight sulfurous compounds in exceedingly large quantities, nitrogenous compounds, high molecular weight organometallic complexes (principally containing nickel and vanadium) and light hydrocarbon-insoluble material. In this regard, black oils `differ considerably from heavy gas oils which are not so severely contaminated, and which normally do not contain appreciable quantities of asphaltic material. A black oil is generally characterized, in the petroleum refining art, as a heavy hydrocarbonaceous material of which more than about 10.0% by volume boils above a temperature of 1050 F., and which has a gravity less than about 20.0 API. Sulfur concentrations are exceedingly high, being more than 1.0% by weight, and often in excess of 3.0%. There currently exists an abundant supply of such hydrocarbonaceous material, the utilization of which, as a source of more valuable distillable hydrocarbon products, is virtually precluded by present-day catalytic reaction techniques.

Knowledgable experts are presently predicting a worldwide energy crisis in the not-too-distant future. For example, those possessing expertise in the field of petroleum exploration are concerned with the ever-dwindling reserve supply of natural gas as compared to the ever-increasing demand therefore. As a result of legislation being imposed upon the sulfur content of liquid fuel oils, burned to meet certain energy requirements, more and more energy suppliers are looking to natural gas as a substitute. Several processes are being proposed which, it is believed, Will alleviate the forthcoming critical shortage of natural gas. These processes generally involve the conversion of naphtha fractions, via steam reforming and shift methanation, into a synthetic natural gas rich in methane. However, this in turn creates a shortage of naphtha boiling range material for ultimate utilization as m-otor fuel. Likewise, a shortage of kerosene boiling range fractions, principally employed as jet fuels, as well as gas oils, will stem from the necessity to convert such charge stocks into suitable automotive fuel. A multitude of factors are, therefore, contributing to the developing 3,830,732 Patented Aug. 20, 1974 ICC energy crisis. Processing technology is required t-o insure the utilization of virtually 100.0% of petroleum crude oil charge stocks. In the petroleum refining art, this is commonly referred to as converting the bottom of the barrel.

'Ihe process encompassed by the present invention supplies at least some of the technology required to approach virtually 100.0% utilization of hydrocarbonaceous black oils for conversion into distillable hydrocarbons. Specific examples Iof those charge stocks to which the present technique is adaptable, include a vacuum tower bottoms having a gravity of 7.1 API and containing 23.7% by weight of an asphaltene-containing fraction; a topped crude oil having a gravity of 11.0 API and containing 10.1% by weight of asphalts; a vacuum bottoms having a gravity of 5.4 API and containing 12.8% by weight of heptane-insoluble asphaltenic material; and, a reduced crude having a gravity of 11.5 API and containing 8.6% by weight of asphaltenic material.

The present invention is directed towards a multiplestage process for effecting the removal of asphaltic material from black oil charge stocks. However, the separation of the metal-containing asphaltic pitch is accomplished in a manner which retains a convertible resin concentrate for subsequent processing in a catalytic reaction zone to increase the volumetric yield of more valuable distillable hydrocarbon products. An important advantage of the present process, as will be recognized by those having skill in the art, is a significantly lower solvent/charge stock volumetric ratio than that heretofore thought to be required in order to reject substantially all the asphaltic material.

OBI ECTS AND EMBODIMENTS A primary object of the present invention is to afford a method for effecting the removal of insoluble asphaltenes from petroleum charge stocks.

Another object is to provide a solvent deasphalting process which retains convertible resins in the solvent-rich hydrocarbon phase. A corollary objective is to effect a decrease in the solvent/ charge stock volumetric ratio while rejecting substantially all insoluble asphaltics.

Therefore, in one embodiment, my invention is directed toward a deasphalting process which comprises the steps of: (a) contacting an asphaltene-containing charge stock with a first selective hydrocarbon solvent, in a first solvent extraction zone, at a solvent/charge stock volumetric ratio less than about 4.0:1.0, to provide a first solventrich liquid phase and a first solvent-lean liquid phase containing resins and asphaltenes; (b) contacting at least a portion of said first solvent-lean phase with a second selective hydrocarbon solvent, containing at least one more carbon atom per molecule than said first selective solvent, in a second solvent extraction zone, to provide a substantially asphaltene-free, resin-containing second solvent-rich liquid phase and an asphaltene-containing second solventlean liquid phase; and, (c) recovering substantially deasphalted oil from said first and second solvent-rich liquid phases.

Other objects and embodiments of my invention 'relate to additional details regarding preferred deasphalting conditions and techniques, and preferred solvents for utilization in the first and second extraction zones. Iir one such other embodiment, the solvent/charge stock volumetric ratio within the first solvent extraction zone is in the range of about 1.0:1.0 to about 4.021,0. In another such embodiment, the temperature in the first solvent eX- traction zone is higher than the temperature in the second solvent extraction zone.

PRIOR ART The deasphalting process encompassed by the present invention makes use of two solvent extraction zones to -vent deasphalting art. With the exception of the specic limitations hereinafter set forth, any suitable solvent deasphalting technique known in the prior art may be employed, several examples of which are found in the references hereinafter briefly described.

Exemplary of a single-stage prior art deasphalting process is found in U.S. Pat. No. 1,948,296 (Class 208-4). The separated asphaltic fraction is admixed With a suitable oil (lubricating oil, gas oil, etc.) and subjected to oxidation in order to obtain a particularly good road-type asphalt product. Suitable solvents are described as including light petroleum hydrocarbon mixtures such as naphtha, and light petroleum fractions comprising propane, n-butane and isobutane, certain alcohols, ether mixtures thereof etc. No mention is made of the solvent/charge stock volumetric ratio, utilized in the solvent extraction zone, and no differentiation is made between the asphaltic material and converible resins.

The broad concept of solvent deasphalting is discussed in U.S. Pat. No. 2,081,473 (Class 208-14). Suggsted suitable solvents include light petroleum fractions, such as naphtha, casinghead gasoline and distillates which are normally vaporous at standard conditions of temperature and pressure. The preferred class of solvents are liquefied normally gaseous hydrocarbons including methane, ethane, propane, butane, or mixtures thereof. The solvent/ charge stock volumetric ratio, within the extraction zone, is not stated and there is no recognition of the difference beween convertible resins and insoluble asphaltics.

An improved single-stage deasphalting technique is described in U.S. Pat. No. 2,587,643 (Class 208-309) wherein the hydrocarbon solvents are utilized in admixture with a modifier comprising an organic carbonate. The solvent contains up to about 20.0% by volume of the modifier, which mixture is utilized in a ratio to the charge stock in the range of about 1.0 to about 15.0.

A similar technique is described in U.S. Pat. No. 2,882,- 219 (Class 20S-86), wherein an aromatic hydrocarbon is added to the charge stock prior to subjecting the same to solvent extraction. The charge stock/ aromatic volumetric ratio is in the range of about 3:1 to about 10:1, while the solvent/charge stock ratio is from about 3:1 to about 15: 1.

U.S. Pat. No. 2,914,457 (Class 208-79) describes a multiple combination process involving fractionation, vacuum distillation, single-stage solvent deasphalting, hydrogenation and catalytic reforming. The preferred solvents, for utilization in the deasphalting zone, include liquefied normally gaseous hydrocarbons such as propane, n-butane, isobutane, as well as ethane, ethylene, propylene, n-butylene, isobutylene, pentane, isopentane and mixtures thereof; the solvent/oil volumetric ratio is indicated as being in the range of about 2.0:1.0 to 10.0:1.0.

A single-stage deasphalting process is describedin U.S. Pat. No. 2,943,050 (Class 208-309) Vwherein a cutter stock is added to the asphaltic raffinate, and the mixture is flashed'to recover the solvent. The solvent/charge stock volumetric ratio is in the range of about 2.0: 1.0 to about .10.0,:1.0.v

' In U.S., Pat. No. 2,975,121 (Class 20S-,251).the asphal- 20S-45) utilizes a double solvent extraction technique in which phenol is admixed with the selective solvent.

The use of a dispersing liquid-Le. glycol-is described in U.S. Pat. No.` 3,321,394 (Class 20S-45); the solvent! char-ge stock ratio, within the single-state extraction zone, is in the range of about 5:1 to about 20: 1.

U.S. Pat. No. 2,002,004 (Class 20S-14) involves a two-stage deasphalting process with intermediate distillation of the solvent-rich hydrocarbon phase from the first solvent extracation zone. The second stage completes the precipitation of asphalts from 'the bottomv stream recovered from the fractionation system.

Another two-stage deasphalting process is described in U.S. Pat. No. 2,101,308 (Class 20S-309). The vfirst solvent extraction system employs gasoline as the solvent, While the second stage utilizes the gasoline-rich extract as the charge stock and sulfur dioxide for the removal of the remaining asphaltics.

U.S. Pat. No. 3,074,882 (Class 208-309), describes a multiple-stage system wherein butane is utilized to precipitate the asphaltic material; the resulting deasphalted oil is subjected to two successive propane fractionation zones at a propane/ deasphalted oil volumetric ratio in the range of about 4:1 to about 12: 1.

Conspicuously absent from such prior art is a recognition of the differentiation to be made between the insoluble asphalticmaterial and the convertible resin concentrate. There exists no awareness of the value of recovering the resin concentrate for subsequent processing in order to increase the volumetric yieldof lower-boiling hydrocarbon products. The multiple solvent extraction zones of the present deasphalting process function to recover a convertible resin concentrate, and the prior art is silent with respect to this operating technique.

With respect to those of the foregoing prior art deasphalting processes which are effected in multiple extraction zones, it must be noted that the second extraction zone precipitate asphaltics from the solvent-rich hydrocarbon phase, recovered from the first extraction zone, rather than the solvent-lean phase. Additionally, the prior art does not appear to be cognizant of the operating techniques which enable a significant reduction in the overall quantity of solvent required to effect the removal of the unconvertible asphaltic residuum.

SUMMARY OF THE INVENTION The deasphalting process, encompassed by the present invention, utilitzes two solvent extraction zones to recover a deasphalted oil containing convertible resins and to reject an asphaltic residuum. The initial solvent extraction technique is carried out at a solvent/charge stock volumetric ratio less than about 4.0:1.0, and other conditions, in order to provide a solvent-lean hydrocarbon phase containing both resins and asphaltic material. This hydrocarbon phase constitutes the charge to the second solvent extraction zone which utilizes a selective solvent containing at least one more carbon atom per molecule than that solvent utilized in the initial solvent extraction zone. When compared to prior art processes of the type hereinbefore described, the present process necessitates the utilization of substantially less solvent to produce a substantially completely deasphalted oil, and simultaneously rejects, as a quasi-product, a significantly lesser amount of the charge stock as the asphaltic residuum.

-From avpractical standpoint, both solvent extraction zones will function at operating conditions within identical ranges.I However, the solvent/ charge stock volumetric ratio employed Within the first solvent extraction zone is less than about 4.0: 1.0, while the selective solvent lutilized in the' second extraction contains at least one more carbon'atomper molecule than the selective solvent em- '.ployed in the first extraction zone. Preferably, the solvent/ charge stock volumetric ratio inthe second solvent extraction zone is greater than the solvent/charge stock ratio in the first extraction zone, whereas the vtempera- V"ture in the' Yfirst extraction zone is higher than the temperrature in vthe second extraction zone. Considering these limitations and preferred extraction techniques, suitable 4extraction conditions include a temperature in the range ofl about 50 F. to about 600 E., and preferably from aboutv 100 F. to about 400 the pressure will be maintained within the range of about 100 to about 1,000 p.s.i.g., and preferably fromabout 200 to about 600 p.s.i.g. The precise operating conditions will generally depend upon the physical characteristics of the charge stock as Wellas the selected solvents. Ingeneral, the temperature and pressure are selected to vmaintain the solvent extractionV operations in liquid phase'and, with respect to the first extraction zone,.to insure that substantially all the convertible resins are removed along with the asphaltenes in the solvent-leanheavy phase, and, with respect to the second extraction zone-,fl to insure that substantially all the asphaltic pitch is removed in `the solvent-lean heavy phase with the resin concentrate being retained within the solvent-rich hydrocarbon phase. Suitable solvents, for utili- .zation in the present combination deasphalting process, mclude those hereinbefore described with respect to prior art deasphalting techniques. Thus, it is contemplated that the solvent will be selected from the group of light hydrocarbons such as ethane, methane, propane, butane, lsobutane, pentane, isopentane, neo-pentane, hexane, isohexane, heptane, the mono-olelinic counterparts thereof, etc. Furthermore, the solvent may be a normally liquid naphtha fraction containing hydrocarbons having about to about 15 carbon atoms per molecule, and preferably a naphtha fraction having an end boiling point below about 200 F. Thus, the selected solvent for utilization in the first extraction zone comprises a hydrocarbon containing from about 1 to about 13 carbon atoms per molecule, while the selective solvent utilized in the second extraction zone comprises a hydrocarbon containing from 2 to about 15 carbon atoms per molecule. A particularly preferred operating technique is to utilize propane as the solvent in the first extraction zone and normal pentane as the solvent in the second extraction zone. The solventrich normally liquid phase, recovered from each of the solvent extraction zones, is introduced into a suitable solvent recovery system, the design and techniques of which are thoroughly described within the prior art. Recovered solvent may, where appropriate and desired, be recycled to the particular extraction zone.

The temperature maintained in the first solvent extraction zone will normally be at least about 20 F greater than that within said second extraction zone. As hereinbefore set forth, the solvent/charge stock ratio within the first reaction zone is less than about 4.0:1.0-i.e. from 1.0:l.0 to about 3.5 :1.0. The solvent/charge stock ratio in the second reaction zone will be greater, and generally in the range of about 1.25: 1.0 to about 10.0: 1.0. The overall quantity of solvent, required to produce a substantially deasphalted oil from a given charge stock, is significantly less than that required by prior art processes to obtain a like degree of asphalt precipitation.

Other conditions and preferred operating techniques will be given in the following description of the present process. 'In further describing this process, reference will be made to the accompanying figure which illustrates one specific embodiment. .In the drawing, the embodiment is presented by means of a simplified ow diagram in which many details such as pumps, instrumentation and controls, heat-exchange and heat-recovery circuits, valving, start-up lines and similar hardware have been omitted as being non-essential to an understanding of the techniques involved. The use of such miscellaneous appurtenances, to modify the process, are well within the purview of one skilled in the art.

DESCRIPTION OF DRAWING The accompanying drawing will be described' in conjunction with a commercially-scaled unit designed to process about 80,000 Bbl/day of vacuum column bottoms. Charge stock analyses indicate a gravity of about 8.0 API, 3.08% by weight of sulfur, 186 weight 6 p.p.m. of metals and an asphaltene-containing fraction in the amount of about 14.8% by weight.

The charge stock, in an amount of 80,000 BbL/day, is introduced, via line 1, into extraction zone 2, wherein it countercurrently contacts propane being introduced by way of line 3, inclusive of make-up propane from line 4. Solvent extraction, at a propane/charge stock volumetric ratio of 2.5:1.0 (200,000 Bbl./day of propane), is effected in substantially liquid phase at a pres-v sure of about 600 p.s.i.g. and a temperature of about 200 =F. A solvent-rich hydrocarbon phase, free from resins and asphaltenes, is withdrawn by way of line 5, while a propane-lean phase, in an amount of about 25,000 BbL/day (exclusive of propane), is removed via line 6.

The solvent-rich phase is sent to solvent recovery system 7, from which propane is recycled by way of line 3. The deasphalted, resin-free oil is withdrawn via line 8. The solvent-lean phase, containing the insoluble asphaltic fraction, convertible resins and some distillable hydrocarbons, continues through line 6 into solvent extraction zone 9. Normal pentane, in an amount of about 100,000 Bbl/day (solvent/oil volumetric ratio of 4.0: 1.0), is introduced via line 10, and is inclusive of makeup pentane from line 11. The pressure is about 600 p.s.i.g., and the temperature about 180 F. A pentane-rich, resincontaining liquid phase is withdrawn by way of line 12, and introduced thereby into solvent recovery zone 13. Recovered solvent is recycled via line 10, while the distillable hydrocarbons and convertible resins are recovered via line 14, admixed with the hydrocarbons in line 8, and continue therethrough as the deasphalted oil product of the process. An asphaltic pitch, in an amount of about 5.9% by weight of the fresh feed charge stock, is removed from the process via line 15.

The substantially asphaltene-free oil in line 8 indicates an asphaltene concentration of about 0.3% by weight and a metals content of about 7.0 p.p.m-. It should be observed that the illustratedI process employed total solvent in an amount of 300,000 Bbl./day, or an overall solvent/charge stock volumetric ratio of about 3.8:1.0. A typical single-stage deasphalting technique, employing, for example, n-butane, results in about 14.0% by weight of an asphaltic pitch, and requires a solvent/ charge stock ratio of about Il0.0:1.0, or 800,000 Bbl./day.

The foregoing illustrates the method of the present invention and the benefits to be afforded through the utilization thereof.

'I claim as my invention:

1. A deasphalting process 'which comprises the steps of:

(a) contacting a hydrocarbon charge stock containing asphaltenes and resins with a dirst selective hydrocarbon solvent, in a first solvent extraction zone, at a solvent/charge stock volumetric ratio less than about 4.0:1.0, and separating a first solvent-rich hydrocarbon liquid phase free from asphaltenes and resins from a first solvent-lean liquid phase containing resins and asphaltenes;

(b) contacting at least a portion of said rst solfventlean phase with a second selective hydrocarbon solvent, containing at least one more carbon atom per molecule than said lirst selective solvent, in a second solvent extraction zone, and selectively dissolving resins in said second solvent to provide a substantially asphaltene-free, second solvent-rich liquid phase wherein substantially all of said resins of said rst solvent-lean liquid phase are retained in said second solvent-rich liquid phase, and an asphaltenecontaining second solvent-lean liquid phase; and

(c) recovering substantially deasphalted oil from said rst and second solvent-rich liquid phases.

2. The process of Claim 1 further characterized in that said solvent/charge stock volumetric ratio is in the range of 'fromI about 1.0:1.0 to about 4.0:1.0.

3. The process of Claim 1 further characterized in that said lirst selective solvent comprises a hydrocarbon containing from one to about thirteen carbon atoms per molecule, and said second selective solvent comprises a hydrocarbon containing from two to about fteen carbon atoms per molecule.

4. The process of Claim 1 further characterized in that the solvent/charge stock volumetric ratio in said second solvent extraction zone is greater than the solvent/charge stock volumetric ratio in said rst solvent extraction zone.

5. The process of Claim 1 further characterized in that the temperature in said rst solvent extraction zone is higher than the temperature in said second solvent extraction zone.

8 6. The process of Claim 1 further characterized in that said dirst selective solvent is propane and said second selective solvent is n-pentane.

References Cited UNITED STATES PATENTS 2,079,886 5/1937 Voorhees 208-309 2,500,757 3/1950 Kiersted 208-309 3,423,308 1/1969 Murphy 208-309 3,627,675 12/ 1971 Ditman et al 208-309 3,074,882 1/1963 Gross et al. 208-309 HERBERT LEVINE, Primary Examiner 

